Hydrolysable silane-terminated polymers are commonly used in the marketplace of adhesives, sealants and coatings. This is at least partially attributed to their environmentally friendly, low volatile organic content characteristics. Certain hydrolysable silane-terminated polymers and their use in sealants, adhesives and coatings have been disclosed in the art. Illustratively, U.S. Pat. No. 3,627,722 discloses polyurethane sealants made from an isocyanate-terminated polymer, wherein at least five percent of the isocyanate groups are end-blocked with trialkoxysilyl groups. U.S. Pat. No. 7,319,128 discloses organyloxysilyl-terminated polymers obtained by reacting hydroxyl-terminated organic polymers with isocyanato-functional silanes in the presence of a catalyst. U.S. Pat. No. 6,001,946 discloses curable silane-terminated polymers based upon maleate-adducts of aminoalkylsilanies.
Unfortunately, as compared with conventional urethane-based adhesives and sealants, cured products made from hydrolysable silane-terminated polymers tend to have lower modulus and tensile strength than might be desired. Efforts have been made to improve the modulus and tensile strength of the products made from the silylated polymers. Illustratively, U.S. Pat. No. 5,990,257 discloses silylated polyurethanes prepared by using extremely low-unsaturation polyether polyols in the formation of the polyurethane prepolymers that are silylated. The '257 patent discloses that these silylated polyurethanes exhibit improved mechanical properties upon curing to a low-tack sealant. Likewise, U.S. Pat. No. 6,498,210 describes a silylated polyurethane polymer containing unreacted isocyanate groups or low molecular weight terminators. The '210 patent discloses that such polymers provide improved tensile strength after cure. Moreover, U.S. Pat. No. 6,001,946 discloses a class of N-silylalkyl-aspartic acid ester-terminated polyurethane polymers and sealant formulations made from the silylated polymers that are said to exhibit improved elongation, tensile strength and tear resistance.
Heretofore, resin compositions employing hydrolysable silane-terminated polymers typically required the use of volatile organic solvents in order to provide a desirable viscosity prior to curing. In order to meet the increasing stringent environmental regulations, efforts have been previously made to reduce the volatile organic content of the resin compositions. For example, U.S. Pat. No. 5,719,251 discloses certain reactive organosilicon compounds that can be used to provide coatings, adhesives, and the like that allegedly have low volatile organic content. However, this patent does not disclose any compositions exhibiting a combination of low volatile organic content and low viscosity before curing and improved modulus and tensile strength after cure.
In the field of hot melt applications, thermoplastic polymers containing tackifiers, fillers and other additives are typically utilized. These hot melt compositions are solid at room temperature but flow at elevated temperatures. Because the compositions are made up primarily of an uncrosslinked thermoplastic component, they are often of low modulus and are susceptible to creep and cold flow under static loads making them unsuitable for many applications where strength of the adhesive joint is critical such as that required for bonding together heavy metal sheets in the construction of truck trailers. The weight on the joints, combined with vibration and environmental heat and moisture resulting from exposure to sun in hot and humid climates, can cause adhesive joints made with known hot melt adhesives to distort and eventually fail.
Moisture-curable hot melt adhesive compositions are known in the art which partially address the foregoing deficiencies. These compositions often contain a thermoplastic component such as a chlorinated paraffin or plasticizer, styrene block copolymer, butyl rubber or poly-α-olefin, and a silylated polyurethane based upon polyols or polyamines containing polybutadiene, polyester, acrylic, polycarbonate or polythioether backbones. Moisture-curable hot melt adhesive compositions contain a continuous phase of the thermoplastic component in which the silylated urethane is dispersed and crosslinked during the application process. The thermoplastic continuous phase, however, remains susceptible to creep and cold flow when placed under static loads. Where the silylated polyurethane component of a moisture-curable holt melt resin composition is incompatible with its thermoplastic component, little if any crosslinking will occur between the two thus giving rise to phase separation of the cured material. Single component and moisture-curable hot melt compositions may therefore exhibit insufficient strength and modulus due to the thermoplastic polymer debonding from the silylated polyurethane under static loads. The silylated polyurethane phase may also be too elastomeric and too low in modulus to provide the desired levels of bond strength.
High strength elastic adhesives can be formulated by using carbon black with high surface area in silylated polyurethane resins such as in SPUR 1050 resin. To achieve tensile strengths up to about 1000 psi, large amounts of carbon black are needed. As a consequence, the compositions are extremely viscous and are difficult to dispense at ambient temperature. One solution to this high viscosity problem is to include in the composition a liquid plasticizer. The use of plasticizer not only lowers the viscosity, but also lowers the tensile modulus and increases elongation. However, conventional non-reactive plasticizers can migrate out of the crosslinked adhesive, especially at elevated temperatures. The loss of plasticizer will result in a more rigid elastomer, not meeting the original application design requirements.
Accordingly, there is a continuing need in the hydrolysable silane-terminated polymers community for a resin composition that is dispensible in an uncured state, has no plasticizer migration, and allows for elongation above 200% while maintaining high modulus and tensile strength. The present invention provides one solution to that need.